Method of preparing curable siloxane polymers containing integral UV absorbers

ABSTRACT

Novel curable siloxane polymers having integral ultra-violet light absorbers are disclosed which are useful in preparing a variety of commercial silicone products requiring excellent resistance to loss of UV protection due to external forces.

The present invention relates to novel curable siloxane polymers. Moreparticularly, the present invention relates to ultra-violet absorbentcurable siloxane polymers. Most particularly, the present inventionrelates to curable siloxane polymers having integral silylatedultra-violet light absorbers and to a novel method of making thesepolymers.

BACKGROUND OF THE PRESENT INVENTION

Protection against ultra-violet (UV) radiation, such as from the sun,has become an important issue in the preparation of personal, householdand automotive products in recent years. Depletion of atmospheric ozonehas led to an increase in the amount of atmospheric UV radiation, andconcurrently has resulted in the need to filter out such harmful rays.

Silicone polishes are commonly used to improve the appearance of, aswell as to protect, household products, luggage, marine and automobilevinyl and the like. While silicone polishes are generally consideredexcellent by those skilled in the art, they suffer from the shortcomingthat when they are prepared by conventional mechanical methods, theultraviolet light absorbing agents contained therein are considered tobe fugitive materials, from the standpoint of various externalconditions such as weathering, abrasion, heating and the like.

Silicones with fugitive UV agents can also be utilized in emulsion formfor use as a treating agent for fabrics, upholstery, carpeting,draperies and the like. Treatment with such silicone emulsions impartswater and dirt repellency to the fabric as well as UV resistance.

It is further known that fugitive UV agents can be added to siliconesfor use in cosmetic applications such as make up, sun tanning lotionsand hair products. Lamb et al., U.S. Pat. No. 5,049,377 teaches the useof UV absorber additives in a hair care composition comprisinghydrophobic cationic emulsions of highly branched and/or crosslinkedpolydimethylsiloxane.

In each of the foregoing applications, while the protection against UVradiation lasts for a finite period of time, due to weathering, abrasionand heating etc. the protection is lost much sooner than desired.Accordingly, attempts have been made in the art to provide a UVabsorbent silicone polymer which has improved resistance to weathering.

Forrestier et al., U.S. Pat. No. 5,089,250, teach abenzotriazole-containing diorganopolysiloxane cosmetic, prepared by ahydrosilation process comprising (i) preparing a benzotriazolederivative by reacting an alkenyl halide with a benzotriazole compound,and then (ii) reacting the benzotriazole derivative with a siliconehydride.

Hill et al., U.S. Pat. No. 4,554,369, teach the preparation oforganosilicon compounds which are useful as sunscreens and which areprepared by reacting an epoxy containing siloxane with the appropriateacid or acid chloride.

Special mention is made of Thimineur et al., U.S. Pat. No. 4,696,969which discloses emulsion polymerized silicone emulsions having siloxanebonded UV absorbers. The patentees teach dispersing the siloxane inwater with an emulsifier, adding the UV agent during emulsionpolymerization of the siloxane to chemically bond the UV agent to theresulting emulsion polymerized polydiorganosiloxane.

It has now been discovered that a novel UV containing curablesilanol-terminated siloxane polymer can be produced, and that suchcompounds have excellent retention of UV resistant properties underconditions of weathering.

SUMMARY OF THE PRESENT INVENTION

According to the present invention there is provided a curable siloxanepolymer containing integral UV stabilizers comprising those of thefollowing general formula ##STR1## wherein each X is the same ordifferent and represents hydrogen, hydroxyl, hydrocarbon or substitutedhydrocarbon or a curable silylated ultraviolet light absorbing agent(hereinafter "curable silylated UV agent") provided at least one of X isa curable silylated UV group, "a" is 0, 1 or 2, and "b" is above about1.

Also according to the present invention there is provided a method ofpreparing a curable siloxane polymer containing integral UV stabilizerscomprising those of the following general formula: ##STR2## wherein eachX is the same or different and independently represents hydrogen,hydroxyl, hydrocarbon or substituted hydrocarbon or a curable silylatedUV agent provided at least one of X represents a curable silylated UVgroup, "a" is 0, 1 or 2, and "b" is above about 1, the methodcomprising:

(a) mixing a solvent and a curable siloxane to form a siloxane mixture;

(b) adding to the siloxane mixture a curable silylated UV agent;

(c) diluting the mixture obtained in step (b) with a co-solvent andmixing to form a solution;

(d) adding a catalyst to the solution and reacting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts in graphic form the UV absorption spectra of a curablesiloxane polymer having integral UV stabilizers according the claims ofthe present invention.

FIG. 2 depicts in graphic form the UV absorption spectra of a fugitiveUV light additive.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The compositions of the present invention are generally prepared byblending the curable silylated UV absorbing agent with asilanol-containing siloxane followed by dilution with co-solvents, andreaction in the presence of a catalyst. The invention will be describedwith regard to linear silanol-terminated siloxanes, although it is to beunderstood that the scope of the invention also includes branchedsilanol-terminated siloxanes and other curable siloxanes.

The linear silanol-terminated, or silanol-chain stopped, siloxanes foruse in the practice of the present invention may be represented by theformula: ##STR3## wherein R¹ and R² are the same or different and areeach independently organic radicals of up to about 20, and typically upto about 8, carbon atoms, selected from hydrocarbyl, halohydrocarbyl andcyano lower alkyl and n is a number that varies generally from about 1to about 10,000, preferably from about 20 to about 3,000, and morepreferably from about 6 to about 1,000.

The silanol-chain stopped polydiorganosiloxanes are well known in theart and they may be prepared by known methods, such as described inBeers, U.S. Pat. No. 3,382,205 and may include compositions containingdifferent R¹ and R² groups. For example, in the formula above, the R¹groups can be methyl, while the R² groups can be phenyl and/orbeta-cyano-ethyl and/or trifluoropropyl. Furthermore, within the scopeof the definition of polydiorganosiloxanes useful in the presentinvention are copolymers of various types of diorgano-siloxane units,such as silanol chain-stopped copolymers of dimethylsiloxane units,diphenylsiloxane units, and methylphenylsiloxane units, or, for example,copolymers of dimethylsiloxane units, methylphenyl-siloxane units andmethylvinyl siloxane units. Preferably, at least 50% of the R¹ and R²groups of the silanol chain-stopped polydiorganosiloxanes are alkyl,e.g., methyl groups.

In the above formula, R¹ and R² can be selected from, for example,mononuclear aryl, halogen-substituted mononuclear aryl, alkyl, alkenyl,alkynyl, haloalkyl, haloalkenyl, haloalkynyl, cycloalkyl, cylcoalkenyl,alkyl and halogen substituted cycloalkyl and cycloalkenyl, and cyanolower alkyl.

Further, it is contemplated that a mixture of various silanol-terminatedpolydiorganosiloxanes may also be employed. The silanol-terminatedpolydiorganosiloxanes employed in the practice of the present inventionmay vary from low viscosity thin fluids to viscous gums, depending onthe value of n and the nature of the particular organic groupsrepresented by R¹ and R² of the above formula.

The viscosity of the silanol-terminated polydiorganosiloxanes thusvaries broadly, e.g., in the range of from about 10 to about 1,000,000cps at 25° C. Preferably it will be in the range of from about 20 toabout 60,000 cps, and especially preferably from about 30 to about10,000 cps at 25° C.

The ultra violet light or radiation absorbing agents useful in thepractice of the present invention are curable silylated UV agents andmay be prepared from a wide variety of known UV agents, such as, forexample, benzophenones, benzotriazoles and aminobenzoic acids, as wellas others which are available commercially and described in theliterature. The UV agent is generally silylated by an addition typereaction with a curable silylating agent. Typically, the curablesilylating agent is a silane of the formula R'_(r) R"_(s) R^(H) _(t) Siwhere R' is alkanoyl, R" is alkyl, R^(H) is hydrogen, "r" is 1, 2, or 3,"s" is 0, 1 or 2, and "t" is 1, 2 or 3, and r+s+t is 4. Particularlyuseful as a silylating agent is triethoxy silicon hydride.

A particularly useful class of ultraviolet light absorbing agents foruse in the present invention is described in Ashby, et al., U.S. Pat.No. 4,278,804. Of course, as stated above, other suitable ultravioletlight absorbing agents effective for practicing the present inventioncan be readily determined by the artisan without undue experimentation.Briefly, Ashby et al. discloses ultraviolet light absorbing agentshaving the formula ##STR4## wherein G is ##STR5## Y is H or OH, Z is H,OH, OQ or OW, where at least one Z is OH if Y is H,

Q is --CH₂ (CH₂)_(m) Si(R³)_(x) (OR⁴)_(y) and

W is --C_(p) H_(2p+1),

where x=0, 1 or 2, y=1, 2 or 3 and x+y =3,

R³ is an alkyl or alkanoyl radical having from 1 to about 6 carbon atoms,

R⁴ is an alkyl radical having from 1 to about 6 carbon atoms,

m=0, 1 or 2 and p=1 to 18.

Especially useful UV light absorbing agents for practice in the presentinvention are compounds having the formulas: ##STR6##

An example of another class of suitable ultraviolet light absorbingagents is silylated paraaminobenzoic acid and its derivatives, forexample, its esters having from 1 to 15 or more carbon atoms. Of course,it is also possible to substitute the hydrogen atoms of the aminoradical with alkyl radicals such as methyl and ethyl. Such silylatedderivatives are generally prepared by an addition type reaction, forexample, according to the reaction equation ##STR7## where each R⁵ isthe same or different and independently represents hydrogen or a loweralkyl radical and R⁶ is a C₁₋₁₅ hydrocarbon radical.

Some other examples of benzophenone and benzotriazole compounds aredescribed in U.S. Pat. Nos. 3,043,709; 3,309,220; 3,049,443 and2,976,259. These may similarly be silylated according to methods wellknown to those skilled in the art, such as the above-described additionmethod.

The amount of siloxane and curable silylated UV agent employed in thepresent invention can vary widely as long as sufficient curablesilylated UV agent is employed to provide improved UV light absorption.Accordingly, the molar ratio of siloxane to curable silylated UV agentmay vary from about 1:1 to about 1:5. The ratio of siloxane and curablesilylated UV agent, and the structure of the siloxane will affect thelocation of substitution of the UV agent on the siloxane. For example, a1:2 molar ratio with a silanol-terminated siloxane will produce apolysiloxane which is terminated with the silylated UV agent, i.e., oneof the formula: ##STR8## wherein each R is the same or different andindependently represents hydrocarbon or substituted hydrocarbon, Brepresents the same or different silylated ultra violet light absorbingagent, and a is 0, 1 or 2, and b is above about 1, and preferably fromabout 1 to about 10,000.

To prepare the compositions of the present invention, the siloxane andcurable silylated UV agent components are typically diluted in thepresence of a solvent and a co-solvent, due to the incompatibility ofthe siloxane and silylated UV agent. The solvent and co-solvent can beany known to those skilled in the art to form a homogeneous solution ofthe siloxane and UV stabilizer.

Particularly useful is a system comprising a hydrocarbon solvent and analcohol co-solvent. Illustratively, the hydrocarbon solvent comprisesnormally liquid aliphatic, cycloaliphatic or aromatic hydrocarbon orhalogenated hydrocarbon compounds of from about 6 to about 15 carbonatoms. These include, but are not limited to, n-heptane, cycloheptane,n-hexane, cyclohexane, benzene, toluene, xylene, styrene, naphthene,methylene chloride and mixtures thereof. The hydrocarbon solvent mayalso comprise polyalpha-olefins and mineral oils such as mineralspirits.

As the co-solvent any of the lower alcohols may be employed, such as,but not limited to, methanol, ethanol, propanol, isopropanol, butanoland the like. A particularly useful system comprises mineral spirits asthe solvent and isopropanol as the co-solvent. Alternatively, theco-solvent may comprise a glycol, such as but not limited to, propyleneglycol, ethylene glycol, and the like.

The amount of solvent and co-solvent employed is not critical, so longas a homogeneous solution of the siloxane and UV light absorbing agentis obtained. Generally, from about 5 to about 50 parts by weight ofsolvent is employed; and from about 5 to about 50 parts by weight ofco-solvent is employed, based on 100 total parts by weight of thesolvent, co-solvent, siloxane and UV agent combined.

A catalyst is then added to the solution containing the siloxane andbenzophenone. The catalysts which are useful in the practice of thepresent invention are those containing an amine group. Convenientlythese may be selected from aminofunctional silanes, quaternary ammoniumsalts, organofunctional amines or aminofunctional siloxanes.

The aminofunctional silanes are known to those skilled in the art. Theseare generally of the formula: ##STR9## where R⁷ and R⁸ are C₁₋₈monovalent hydrocarbon radicals, "u" varies from 0 to 3 and Z' is anamine group or a saturated, unsaturated or aromatic hydrocarbonfunctionalized by an amino group.

Preferred compounds within the formula above are for instance,3-(2-aminoethylamino)propyltrimethoxy silane,gamma-aminopropyltriethoxysilane and gamma-aminopropyltrimethoxysilane.Other aminofunctional silane catalysts that can be utilized in theinstant invention are as follows: gamma-aminopropylmethyldiethoxysilane;gamma-aminopropylmethyldimethoxysilane;bis(3-(triethoxysilyl)propyl)amine;bis(3-(triethoxysilyl)propyl)ethylenediamine;3-(2-aminoethylamino)-propyldimethoxy-t-butoxysilane;methacryloxyethylaminopropyltrimethoxysilane;methylaminopropyltrimethoxysilane; methylaminopropyltriethoxysilane;(N,N-dimethyl-3-amino)propyltrimethoxysilane;N,N-dimethylaminophenyltriethoxysilane; andN,N-dimethylaminoethyldimethoxysilane.

The quaternary ammonium salts useful in the practice of the presentinvention as catalysts are also well known to those of ordinary skill inthe art, who will recognize that certain of these compounds are alsouseful as surfactants. Illustratively, these include, but are notlimited to methylpolyoxyethylene (15) cocoammonium chloride anddimethylsoyammonium chloride, commercially available as Ethoquad® C/25and Arquad® 2-S75 from Armak Company, respectively.

Likewise, the organofunctional amines are also well known to thoseskilled in the art. Typically they are saturated, unsaturated oraromatic hydrocarbons which are functionalized by an amino group.Generally, they can include those of the formulae R⁹ NH₂, R⁹ ₂ NH or R⁹₃ N where each R⁹ is independently the same or different alkyl, alkenylor aryl group. Exemplary of useful amines include, but are not limitedto, methylamine, diethylamine, tri-n-propylamine, cyclohexylamine,benzylamine, ethylenediamine, phenylethylamine, aniline, toluidine andthe like.

The amount of catalyst employed in the present invention typicallyvaries from about 0.05 to about 1 weight percent, preferably from about0.1 to about 0.5 weight percent, and more preferably from about 0.1 toabout 0.25 weight percent, based on the total weight of the siloxane, UVagent, solvent and co-solvent combined.

The mixture of the silanol terminated siloxane, UV agent, solvent,co-solvent and catalyst are then agitated, and the solvents readilyevaporated to form the UV-containing curable polysiloxanes of thepresent invention. It is also contemplated that the mixture may beheated during reaction, although heating is not necessary.

The siloxanes of the present invention are curable, and can be employedin a wide variety of personal care, household and automotive products,as is known to those skilled in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention. They are not tobe construed to limit the scope of the claims of the present inventionin any manner whatsoever.

EXAMPLES 1-3

Three benzophenone-containing silanol-terminated polydimethylsiloxanesare prepared according to the following procedure. Mineral spiritssolvent and linear polydimethylsiloxane fluid are charged to a vesseland agitated for 30 minutes. To the vessel is then charged2,4-dihydroxybenzophenone derivative (silicone triethoxy substituted),and the mixture is agitated for 2 additional hours until uniform. Whenthe mixing is complete, isopropyl alcohol is added to the mixture, andmixing continues for 30 minutes until a homogeneous clear solution isobtained.

To the solution is then added 1 percent by weight ofaminopropyltriethoxy silane catalyst, with agitation for one hour. Thereis obtained a UV containing curable siloxane according to the presentclaims. The compositional data of the three examples prior to catalystaddition is set forth below in Table 1.

                  TABLE 1                                                         ______________________________________                                        Example   1             2      3                                              ______________________________________                                        PDMS.sup.a                                                                              49.0          --     --                                             PDMS.sup.b                                                                              --            48.2   --                                             PDMS.sup.c                                                                              --            --     17.4                                           SHBP.sup.d                                                                               1.0           1.8   32.6                                           MS.sup.e  37.5          37.5   37.5                                           IPA.sup.f 12.5          12.5   12.5                                           ______________________________________                                         .sup.a = Linear silanol terminated polydimethylsiloxane fluid having          average molecular weight of 40,000 and viscosity of 3,000 cps at              25° C.                                                                 .sup.b = Linear silanol terminated polydimethylsiloxane fluid having          average molecular weight of 22,000 and viscosity of 1,000 cps at              25° C.                                                                 .sup.c = Linear silanol terminated polydimethylsiloxane fluid having          average molecular weight of 450 and viscosity of 40 cps at 25° C.      .sup.d = 2,4dihydroxybenzophenone derivative                                  .sup.e = Mineral spirits                                                      .sup.f = Isopropyl alcohol                                               

EXAMPLE 4

The UV absorption of the siloxane polymer of Example 3 is determined byplacing a 0.5 mm cell of 144 mg of polymer per liter of isopropylalcohol and testing in a Cary UV Spectrometer, Model 2400. Forcomparative purposes, a 0.5 mm cell of 50 mg of2,4-dihydroxybenzophenone per liter of isopropyl alcohol is also tested.

The results are set forth in FIGS. 1 and 2, respectively.

From the results it can be seen that the siloxane polymers of thepresent invention exhibit substantially the same UV band absorptioncharacteristics as the fugitive UV additive. The intensity differencesare due to the molecular weight differences of the active UV species.

The above-mentioned patents are all hereby incorporated by reference.

Many variations of the present invention will suggest themselves tothose of ordinary skill in the art in light of the above-detaileddescription. For example, other silylated benzophenones or silylatedpara-amino benzoic acids may be employed as the UV agent. Further, anyof the aminofunctional catalysts such as3-(2-aminoethylamino)propyltrimethoxy silane, gammaaminopropyltrimethoxysilane, methylpolyoxyethylene (15) cocoammonium chloride,dimethylsoyammonium chloride, amino functional polydimethylsiloxanes andtri-n-propylamine may be used. All such obvious modifications are withinthe full intended scope of the appended claims.

We claim:
 1. A method of preparing a curable siloxane polymer containingintegral UV stabilizers comprising those of the following generalformula: ##STR10## wherein each X is the same or different andrepresents hydrogen, hydroxyl, hydrocarbon or substituted hydrocarbon ora curable silylated ultraviolet absorbing group provided at least one ofX is a curable silylated ultraviolet absorbing group, a is 0, 1 or 2,and b is above about 1, said method comprising:(a) mixing a curablesolvent and a siloxane to form a siloxane mixture; (b) adding to saidsiloxane mixture a curable silylated UV agent; (c) diluting the mixtureobtained in step (b) with a co-solvent and mixing to form a solution;(d) adding a catalyst selected from aminofunctional silanes, quaternaryammonium salts, organofunctional amines or aminofunctional siloxanes tosaid solution and reacting.
 2. A method as defined in claim 1 whereinsaid solvent a liquid hydrocarbon.
 3. A method as defined in claim 1wherein said solvent comprises mineral spirits.
 4. A method as definedin claim 1 wherein said siloxane comprises units of the general formula:##STR11## wherein R¹ and R² are the same or different and are eachindependently organic radicals of up to about 20 carbon atoms and "n" isa number ranging from about 1 to about 10,000.
 5. A method as defined inclaim 4 wherein said siloxane comprises linear silanol-terminatedpolydimethylsiloxane.
 6. A method as defined in claim 1 wherein saidsilylated UV agent comprises a silylated benzophenone of the generalformula ##STR12## wherein G is ##STR13## Y is H or OH, Z is H, OH, OQ orOW, where at least one Z is OH if Y is HQ is --CH₂ (CH₂)_(m) Si(R³)_(x)(OR⁴)_(y) and W is --C_(p) H_(2p+1),where x=0, 1 or 2, y=1, 2 or 3 andx+y=3, R³ is an alkyl or alkanoyl radical having from 1 to about 6carbon atoms , R⁴ is an alkyl radical having from 1 to about 6 carbonatoms, m=0, 1 or 2 and p=1 to
 18. 7. A method as defined in claim 6wherein the silylated benzophenone is a compound of the formula:##STR14## or a mixture thereof.
 8. A method as defined in claim 1wherein said co-solvent comprises isopropyl alcohol.
 9. A method asdefined in claim 1 wherein said catalyst comprises an aminoorganosilane.10. A method as defined in claim 9 wherein said aminoorganosilanecatalyst comprises aminopropyltriethoxy silane.